The thing nobody tells you about gray boxes is that the color you picked under shop lighting is never the color you get at home. A gray that looked cool and steely on the shelf turns warm and almost beige under a lamp come five o'clock, and a gray that looked soft and chalky turns cold as a January pond once it's sitting on an open shelf against white walls. I've sent two boxes back for this exact reason and felt foolish both times, because the box hadn't changed, my kitchen light had.
Over time the finish tells on itself. A matte painted fiberboard box will scuff pale at the corners within a year, especially if it gets pulled in and out from under a bed or off a shelf, and no amount of careful handling stops that, it just slows it. A fabric covered box holds its color longer but picks up dust in the weave, so it wants a once a month going over with the soft brush attachment on the vacuum, not a cloth, a cloth just grinds the dust in. Woven paper or seagrass dyed gray fades fastest of all in direct sun, so keep those off the windowsill no matter how good they look catching the afternoon light. Lids with structure, a stiffened board rather than soft fabric, keep their shape for years. Lids without that structure start to dish in the middle, and then they stop sitting flush, and then everything stacked on top leans a little, which bothered me far more than it should have.
If you're starting with nothing, get a mid gray in a sturdy fiberboard with a lid that has some rigidity to it, nothing fancy, just something that doesn't bow when you press two fingers on the middle of it. That one box in a middling gray goes with almost anything you add later, lighter grays, charcoal, even a stray wicker basket that doesn't match and never will.
The day it arrives, check the inside seams and the underside, that's where cheap construction shows first, loose stitching or glue that's already gone a bit yellow. Press the sides in gently too, a box that flexes and holds its shape is doing its job, one that crumples is going to look tired within months.
A true middle gray, neither warm nor icy, is the one that's never let me down in any room I've put it in.